Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 7  |  Issue : 4  |  Page : 509-513

Pressure support ventilation versus spontaneous ventilation in infants undergoing brachial plexus exploration: a comparative study


1 Department of Anesthesia, ICU and Pain Management, Cairo, Egypt
2 Department of Orthopedics, Faculty of Medicine, Cairo University, Cairo, Egypt

Date of Submission16-Jan-2014
Date of Acceptance10-Feb-2014
Date of Web Publication28-Nov-2014

Correspondence Address:
Sherif M Soaida
Department of Anesthesia, ICU, and Pain Management, Faculty of Medicine, Cairo University, Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-7934.145683

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  Abstract 

Background
General anesthesia and muscle relaxants have the potential to decrease or even abolish action potentials, interfering with surgical nerve exploration. Prolonged surgeries in spontaneously breathing infants lead to muscle fatigue, shallow breathing, and CO 2 accumulation. This randomized study aimed to evaluate the efficiency of pressure support ventilation (PSV) in infants undergoing brachial plexus exploration without muscle relaxants in maintaining normal end-tidal CO 2 (EtCO 2 ) and hemodynamics.
Patients and methods
After the approval of the ethical committee in Kasr Al Ainy University Hospital, and parents' consent, 16 ASA I and II infants (4-12 months) were allocated randomly to two main groups. In group I, PSV was used from the start. In group II, spontaneous ventilation was started, followed by switch to PSV once fatigue occurred; group II was subdivided into group IIa (spontaneous ventilation) and group IIb (PSV). Recorded variables included tidal volume, EtCO 2 , oxygen saturation, respiratory rate (RR), heart rate (HR), blood pressure, and arterial blood sample analysis.
Results
Systolic and diastolic blood pressure and HR were higher in group IIa than group I (P = 0.0047, 0.0135, and 0.3575, respectively). EtCO 2 and RR were also higher (P < 0.05). Vt was higher in group I (P = 0.0092). Comparing groups IIa and IIb, systolic and diastolic blood pressure, HR, RR, EtCO 2, and PaCO 2 were significantly higher in group IIa (P < 0.05). Vt was higher in group IIb (P = 0.0053).
Conclusion
PSV in infants undergoing prolonged surgery without muscle relaxants is efficient in maintaining normal EtCO 2 and hemodynamics through avoidance of fatigue and maintaining normal Vt .

Keywords: brachial plexus exploration, infants, nerve surgery, pressure support ventilation


How to cite this article:
Soaida SM, Hanna MG, Youssef MM, Mahmoud M. Pressure support ventilation versus spontaneous ventilation in infants undergoing brachial plexus exploration: a comparative study. Ain-Shams J Anaesthesiol 2014;7:509-13

How to cite this URL:
Soaida SM, Hanna MG, Youssef MM, Mahmoud M. Pressure support ventilation versus spontaneous ventilation in infants undergoing brachial plexus exploration: a comparative study. Ain-Shams J Anaesthesiol [serial online] 2014 [cited 2019 Sep 22];7:509-13. Available from: http://www.asja.eg.net/text.asp?2014/7/4/509/145683


  Introduction Top


The use of muscle relaxants may affect intraoperative neuromonitoring, which is needed during nerve exploration. This is why surgical exploration and repair of the brachial plexus necessitates not using neuromuscular blocking agents. General anesthesia and muscle paralysis have the potential to decrease or even abolish the action potentials, suggesting nerve damage although the conduction system is actually intact [1].

The current standard anesthesia practice during such surgeries is the use of spontaneous ventilation, which has the drawback of carbon dioxide retention resulting from muscle fatigue. Prolonged surgeries in spontaneously breathing infants may also lead to muscle fatigue with shallow breathing and carbon dioxide accumulation.

Pressure support ventilation (PSV) is a pressure-targeted mode that provides breath-by-breath ventilation support, always initiated by the patient and synchronized with the respiratory effort [2,3]. The basic idea behind PSV is to support spontaneous breathing by applying pressure to the airway in response to patient-initiated breaths. PSV is patient triggered and either flow or time cycled. For PSV to be of value during clinical anesthesia, the patient must be breathing spontaneously.

PSV is effective in eliminating the extra work of breathing (endotracheal tube, breathing circuit, and ventilator) while also maintaining the patient's spontaneous ventilation [4-7]. Another advantage of the use of PSV is that it requires less pressure to achieve the same target tidal volume (Vt ) than controlled mechanical ventilation (CMV) [1, 2, 8, 9].

In addition, the resulting reduced intrathoracic pressure attenuates the effects of mechanical ventilation on hemodynamics and cardiac output, especially in neonates [10,11].

Studies in this field focused on the use of PSV with laryngeal mask airway in day-case surgeries, assessing leaks, gastric filling, and gas exchange mostly in adults [12,13]. Other studies focused on its use in ICU [3, 7, 8].


  Aim of the work Top


Our study aimed to evaluate the efficiency of PSV in infants undergoing brachial plexus exploration without the use of muscle relaxants, in maintaining normal end-tidal carbon dioxide (EtCO 2 ) levels and hemodynamic stability through reduction of muscle fatigue.


  Patients and methods Top


This study was carried out at Abu Al Reesh Pediatric Hospital, Cairo University. Sixteen ASA I and II infants aged 4-12 months of both sexes with brachial plexus palsy (because of iatrogenic injury during birth) scheduled for brachial plexus exploration under general anesthesia without a muscle relaxant, as required by the orthopedic surgeon, were allocated randomly to two main groups, eight patients each, by a computer-generated list of random numbers and concealed in closed envelopes.

Group I: PSV was used from the start.

Group II: spontaneous ventilation was started. If fatigue occurred at any time, a switch was made to PSV. Thus, this group was subdivided into group IIa (spontaneous ventilation) and group IIb [pressure support (PS)].

A written consent was obtained from the parents or the legal guardians along with the approval of our hospital's ethics committee.

In both study groups, basic monitors (ECG, noninvasive blood pressure, and pulse oximeter) were inserted; inhaled anesthetic induction was performed with sevoflurane on all patients using the Jackson Rees breathing circuit. After intravenous access was obtained, atropine (0.01 mg/kg) and fentanyl (1 μg/kg) were administered. Endotracheal intubation was carried out using an uncuffed endotracheal tube ranging in size from 3.5 to 4.0 mm according to age. Arterial cannula was then inserted into the radial artery of the contralateral limb or the dorsalis pedis artery for arterial blood gas sampling.

In group I, after the endotracheal tube was placed and the patient had started to take spontaneous breaths, the anesthesia circuit was connected to the anesthesia machine with the PSV mode (Aspire 7900, Datex-Ohmeda; GE Healthcare, Helsinki, Finland). The ventilator variables were adjusted so that the least PS above the positive end-expiratory pressure level would achieve a tidal volume of 5-8 ml/kg. The least flow trigger that the anesthesia machine would supply (0.2 l/min) was started with and increased while ensuring that each trigger initiation was motivated by the patient's respiratory effort as detected in the abdominal region (between the xiphoid process and the umbilicus) to avoid auto triggering. If PSV became insufficient, indicated by an increase in EtCO 2 and/or decreased tidal volume, we administered a muscle relaxant and a switch was made to CMV after coordinating with the surgeon.

In group II, after the endotracheal tube was placed and the patient had started to take spontaneous breaths, the anesthesia circuit was connected to the same anesthesia machine and left on the spontaneous mode. Once a critical point was reached where fatigue occurs [EtCO 2 increases above 50 mmHg, tidal volume reduces to less than 5 ml/kg, and respiratory rate (RR) increases beyond 30/min], we shifted to the PS mode, which was adjusted in the same manner as in group I.

By the end of surgery, all patients were extubated and transferred to the recovery area, where basic monitors were applied for 1 h. Then, patients were transferred to the postoperative care unit for overnight monitoring following this lengthy procedure.

The following variables were continuously monitored and recorded at half an hour intervals: inhaled and exhaled tidal volume, EtCO 2 , peripheral oxygen saturation, RR, heart rate (HR), and arterial blood pressure. Arterial blood sample analysis was carried out every hour (PaO 2 , PCO 2 , pH, and HCO 3 ).

Sample size calculation

A previous study indicated that the mean ± SD of EtCO 2 in the PSV group was 42.8 ± 5.8, whereas in the spontaneous group, it was 50.4 ± 4. On the basis of these data, a total of 16 patients were found to be adequate to achieve a study power of at least 0.8 with an a-error of 0.05 (two-sided).

Statistical analysis

Data were statistically described in terms of mean ± SD. Comparison of numerical variables between the study groups was performed using the Student t-test for independent samples. The data were considered significant if the P-value was less than 0.05. All statistical calculations were carried out using computer programs SPSS version 15 for Microsoft Windows (Statistical Package for the Social Science; SPSS Inc., Chicago, Illinois, USA).


  Results Top


The demographic data of the 16 patients in both study groups are presented in [Table 1], showing no statistically significant difference in age, weight, sex, and duration of surgery. None of the patients in group I needed a rescue change in ventilation mode. However, all patients in group II needed a rescue change in ventilation mode from spontaneous ventilation to PSV, alleviating the need to subdivide this group. The mean onset of change from spontaneous mode to PS mode in group II was 101.88 ± 24.36 min.
Table 1 Demographic data

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The mean PS that we used was 14 cmH 2 O, with minimum and maximum values ranging from 12 to 16 cmH 2 O to produce a 5-8 ml/kg tidal volume. Comparison of systolic (SBP) and diastolic blood pressure (DBP) in groups I and II (before rescue ventilatory change) indicated a higher blood pressure in group II compared with group I. There was a highly significant difference in SBP (P = 0.0047), and a significant difference in DBP, with a P-value of 0.0135. HR was found to be higher in group II (before rescue ventilatory change) than in group I, with no statistical significance (P = 0.358). Peripheral oxygen saturation was slightly higher in group I, with no statistical difference.

EtCO 2 was significantly lower in group I, with a P-value of 0.0002. Also, RR was significantly lower and tidal volume was significantly higher in group I (P = 0.0164 and 0.0092, respectively; [Table 2].
Table 2 Clinical variables of group I and group II (before rescue ventilatory change)

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Comparison of the arterial blood gas analysis for both group I and group II (before rescue ventilatory change) indicated a significant difference in pH, being higher in group I than in group II (before rescue ventilatory change), with a P-value of 0.0228. Also, PaCO 2 was significantly lower in group I (P = 0.0002). Otherwise, there was no significant difference between both groups ([Table 3]). Peripheral oxygen saturation was slightly higher in group I, with no statistical significance.
Table 3 Arterial blood gas analysis differences between group I and group II (before rescue ventilatory change)

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Comparison of SBP and DBP in group II before and after applying rescue ventilatory changes indicated higher blood pressure during the spontaneous ventilation period. There was a highly significant difference in SBP and DBP (P = 0.0054 and 0.0124, respectively). HR was found to be higher before changing to ventilation mode, with no statistical significance (P = 0.232). EtCO 2 and RR were significantly lower and tidal volume was significantly higher in group II after application of ventilatory change (P = 0.0023, 0.0002, and 0.0053, respectively).

Comparison of the arterial blood gas analysis in group II before and after application of rescue ventilatory changes indicated a significant difference in pH, being higher after application of changes (P = 0.0255). Also, PaCO 2 was significantly lower after ventilation changes (P = 0.0003).


  Discussion Top


Our study shows that PSV provides the benefits of mechanical ventilation while retaining the advantages of spontaneous breathing in infants aged 4-12 months undergoing brachial plexus exploration. PSV prevented respiratory muscle fatigue, maintained EtCO 2 within normal limits, maintained tidal volume 5-8 ml/kg, and maintained normal blood gases and hemodynamics. None of the patients in group I (PSV) needed conversion to CMV throughout the procedure, whereas all patients in group II needed a shift from spontaneous ventilation to PSV at some time.

In a study carried out by Tokioka et al. [9] on six children aged 3-5 years in the postoperative period after cardiac surgery, different levels of PS were used, and the tidal volume, minute volume, airway pressure, and RR were measured. They reported that the mechanical work of breathing decreased with higher levels of PS (10 cmH 2 O), thus concluding that PSV can effectively augment spontaneous breathing and reduce the work of breathing in children.

In another study carried out by Tokioka et al. [8] on nine neonates who underwent surgery for congenital heart disease, where PSV was applied to the neonates in the postoperative period to augment spontaneous breathing and improve the synchrony between the thoracic cage and abdominal motions, three levels of PSV were adjusted in these patients on continuous positive airway pressure (CPAP), where high airway resistance caused by small endotracheal tubes resulted in rapid respiratory frequency and patient-ventilator asynchrony. PSV was found to increase the tidal volume and decrease the respiratory frequency associated with an increase in minute ventilation compared with spontaneous breathing without any support.

They also found that PSV improved the thoraco-abdominal synchrony and paradoxical movement of the thoracic cage in neonates. Although the age group that Tokioka et al. [8] studied was younger than that in our study, the benefits of this ventilation mode proved augmenting to the spontaneous breathing. Our study also differs from the latter in that we used a closed-circuit anesthesia machine and not an intensive care ventilator. The anesthesia machine yields a lower peak flow and a longer time delay in delivering this flow.

Garcia-Fernandez et al. [14] investigated the use of PSV in 60 ASA I and II patients aged 2 months to 14 years (divided into three groups according to weight) who were scheduled for day-case surgery with the use of laryngeal mask airway. They found that the PS needed in children weighing 10 kg or less to provide a tidal volume 10 ml/kg was 15 cmH 2 O above the positive end-expiratory pressure level, with maximum and minimum values ranging from 13 to 15 cmH 2 O. This is almost in agreement with our findings, where the mean PS we used was 14 cmH 2 O, with a maximum 16 cmH 2 O and a minimum 12 cmH 2 O, to produce a 5-8 ml/kg tidal volume.

The mean EtCO 2 obtained by Garcia-Fernandez et al. [14] for children weighing 10 kg or less was 42.8 ± 1.14, which is close to the upper physiological limit, whereas the EtCO 2 obtained in our study was 31.33 ± 3.10 in group I and 31.35 ± 3.001 in group IIb. This difference in EtCO 2 between both studies was possibly a result of the greater artificial ventilatory dead space attained by adding the laryngeal mask airway, spirometer, and humidifier in dissimilarity to the dead space present with the solely used endotracheal tube in our study.

Bosek et al. [13] investigated 20 adult patients, 52 ± 11 years of age, planned for surgery under inhalational anesthesia without a muscle relaxant. Patients were allowed to respire spontaneously at atmospheric pressure for 15 min and then randomly received interchanging 15 min trials of PS adjusted to deliver either 5 cmH 2 O or a level titrated to yield a tidal volume of 8 ml kg/body weight. They found that when the PS was titrated to yield a normal tidal volume, the effectiveness of spontaneous breathing was enhanced by reducing the respiratory frequency and PaCO 2 while maintaining hemodynamic homeostasis. These findings are in line with ours.

Von Goedecke et al. [15] compared the efficiency of PSV with CPAP in 20 anesthetized ASA I children 1-7 years of age performed using the ProSeal laryngeal mask airway. Ten patients underwent CPAP, PSV, and CPAP, in order. The other 10 underwent PSV, CPAP, and PSV, in order. Each ventilatory mode was continued for 5 min. PSV had lower EtCO 2 (46 ± 6 vs. 52 ± 7 mmHg; P = 0.001) and slower RR (24 ± 6 vs. 30 ± 6/min; P = 0.001), whereas there were no differences in SpO 2 , mean arterial blood pressure, and HR.

A limitation of our study is that all the children who we studied were infants classified as ASA I and II; thus, our results cannot be generalized to elderly patients and those with respiratory diseases.

Recommendations

More studies are needed involving a larger population, different age groups, and critically ill patients. We recommend that PSV should be used on a wider scale in anesthesia as it is an easy-to-use mode that prevents fatigue in spontaneously breathing anesthetized pediatric patients, and provides better patient-ventilator synchrony.


  Conclusion Top


PSV in infants undergoing prolonged surgery without the use of muscle relaxants plays an important role in maintaining normal EtCO 2 levels and hemodynamics through reduction of the work of breathing and maintaining a normal tidal volume.


  Acknowledgements Top


 
  References Top

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